A vehicle occupant restraint apparatus which includes an inflatable vehicle occupant restraint, such as an air bag, further includes an inflator. When the inflator is actuated, it rapidly emits a large volume of inflation fluid which is directed into the restraint to inflate the restraint. The restraint then restrains an occupant of the vehicle from forcefully striking parts of the vehicle as a result of the collision.
Such an inflator may have a combustion chamber containing an ignitable gas generating material. When the inflator is actuated, the gas generating material is ignited and rapidly generates a large volume of gas for inflating the restraint. The inflator may alternatively comprise a pressure vessel containing a stored quantity of inflation fluid under pressure. The inflation fluid is released to flow from the pressure vessel to the restraint when the inflator is actuated. Inflators are also known to have combinations of pressurized inflation fluid and ignitable material. In each case, the inflator has an electrically actuatable initiator which initiates a flow of inflation fluid from the inflator upon the occurrence of a vehicle collision.
The initiator typically comprises a squib containing pyrotechnic material. The squib is connected with a sensor that senses vehicle conditions indicative of a vehicle collision. If the sensor senses a collision-indicating condition of a predetermined threshold value, it directs electric current through the squib to actuate the squib. The pyrotechnic material in the squib is then ignited. As a result, the ignitable material is ignited and/or the pressurized inflation fluid is released from its container.